The creation and maintenance of online production communities depend on the complex ecology created by the interaction of social roles, and these roles are essential for the governance of the community. This study investigates the organizational structure of one of the most notable peer-production projects: Wikipedia. While online communities have often been depicted as 'flat' and egalitarian, recent studies of Wikipedia suggest that it has developed a cumbersome beaurocratic structure that includes a hierarchy of organizational role. The objective of this study is, thus, to empirically study the organization of roles in Wikipedia and the hierarchy formed through their power relationships. Our research method employs Wikipedia's formal set of access privileges as indicators of roles, and analyses all 4,902,643 Wikipedia members (of which 10,496 hold special access privileges). Applying statistical techniques traditionally employed to validate the psychometric properties of scales, we find that Wikipedia has an intricate ecology of roles. Our analysis of power relationships within these twelve roles reveals Wikipedia's organizational hierarchy. Implications for theory and practice are discussed.